Secondary batteries are devices capable of storing energy in chemical form and of converting into electrical energy to generate electricity when needed. The secondary batteries are also referred to as rechargeable batteries because they can be recharged repeatedly. Common secondary batteries include lead accumulators, NiCd batteries, NiMH accumulators, Li-ion batteries, Li-ion polymer batteries, and the like. When compared with disposable primary batteries, not only are the secondary batteries more economically efficient, they are also more environmentally friendly.
The secondary batteries are currently used in applications requiring low electric power, for example, equipment to help the start-up of vehicles, portable devices, tools, uninterruptible power supplies, and the like. Recently, as the development of wireless communication technologies has been leading to the popularization of portable devices and even to the mobilization of many kinds of conventional devices, the demand for the secondary batteries is dramatically increasing. The secondary batteries are also used in environmentally friendly next-generation vehicles such as hybrid vehicles and electric vehicles to reduce the costs and weight and to increase the service life of the vehicles.
Generally, the secondary batteries have a cylindrical, prismatic, or pouch shape. This is associated with a manufacturing process of the secondary batteries in which an electrode assembly composed of an anode, a cathode, and a separator is mounted in a cylindrical or prismatic metal case or a pouch-shaped case of an aluminum laminate sheet, and in which the case is filled with electrolyte. Because a predetermined mounting space for the electrode assembly is necessary in this process, the cylindrical, prismatic or pouch shape of the secondary batteries is a limitation in developing various shapes of portable devices. Accordingly, there is a need for a secondary battery of a new structure that is easily adaptable in shape.
To fulfill this need, suggestions have been made to develop linear batteries having a very high ratio of length to cross-sectional diameter. Korean Patent Publication No. 2005-0099903 discloses a thread-type flexible battery comprising an inner electrode, electrolyte, and an outer electrode, however has a limited structure of one anode and one cathode and consequently a low capacity balance. Korean Patent No. 0804411 discloses a linear battery comprising a plurality of anodes and a plurality of cathodes with separators interposed therebetween. Korean Patent Registration No. 0742739 discloses a thread-type flexible battery including cathode threads and anode threads, however this is not based on an outer/inner electrode structure.